10. HADRIANA or TRAJANA[248] (A.D. 120), and ALEXANDRINA (?). The sources of this are under La Colonna, about three miles from Gabii. The _specus_ is carried on a fine arcade for two or three miles between the two great roads. The same water was afterwards used for the Felice, with the exception of one of the springs, which was found to be of a petrifying quality, and had choked up the _specus_ of the old aqueduct. It seems probable that the stalactite produced by the petrifying spring had choked up the _specus_ of Trajan and Hadrian before the time of Alexander Severus, that he restored it to use, and it was then called by his name. The construction of the Piscina and Castella Aquæ near the source is distinctly of the time of Hadrian, but in some parts the arcade which carries the _specus_ is of the time of Alexander Severus. 11. SEVERIANA[249] (A.D. 190). The sources of this are in a swampy ground on the lower part of one of the Alban Hills, under Marino and Grotta Ferrata, nearly the same as those of the small river Almo, and the Tepula and Julia. The course is at first underground as far as the Torre di Mezza Via di Albano; from thence it is carried on a fine arcade of the third century to the Villa de Quintilii, and from thence into Rome for the Thermæ of Aurelius Commodus and Septimius Severus, near the Porta Latina. 12. ALEXANDRINA (?)[250]. There is some doubt about the source and the line of this aqueduct. 13. ALGENTIANA[251]. This aqueduct went to the Thermæ of Diocletian, where the _specus_ has been found, but it is almost the same as the last. Both were probably branches from the great early aqueducts. 14. AQUA FELICE[252], A.D. 1587. Made by the Pope, Felice Peretti, or Sixtus V. Its source is the same as that of the Hadriana, which was mistaken in his time for the celebrated Aqua Marcia. 15. AQUA MARCIA PIA. The real old Marcian water was brought into Rome by a Company in 1860-70. The course as far as Tivoli is in a stone _specus_, like the old aqueduct, but after it reaches the level ground it is carried in cast-iron pipes on the other side of the river Anio, and passes under it by a great syphon. This was to avoid repeating the great circuit made by the old aqueduct, and was also done to escape the necessity of crossing the mouths of the number of small streams that fall into the river Anio and drain the Campagna; these are often flooded in the wet season, and would have been likely to injure the bridges of the aqueducts where they crossed the stream; the iron pipes avoid them by being on the other side of the river. MAP OF THE AQUEDUCTS ON THE WESTERN SIDE OF ROME[253]. [Illustration: MAP OF THE AQUEDUCTS ON THE WESTERN SIDE OF ROME Whiteman & Bass, _Photo-Litho’ to the Queen_, 236, Holborn]